You may wish to run this from crontab after copying otrs_backup.sh to /usr/local/bin:

0 20 * * * /usr/local/bin/otrs_backup.sh

This will run at 10pm each night - theoretically you could run it more frequently. OTRS databases will a lot of attachments get quite large though so be mindful of that (I have a couple I manage that are 1GB and are only 5 months old)